Drinking coffee with meals can worsen iron deficiency and may help explain persistent tiredness in some women, experts have warned. Coffee and tea contain polyphenols that can bind to iron in the gut, reducing the amount absorbed into the bloodstream.
The effect is particularly important for people who are already short of iron, rather than being a cause of deficiency on its own. Professor Toby Richards, of the University of East London, said: “If you’re low on iron, the worst thing you can do is wash your meals down with a coffee.”
Iron is needed to transport oxygen around the body and to help cells convert food into usable energy. Low levels can be linked to heavy blood loss, including during periods, while people with inflammatory bowel disease or coeliac disease are also more vulnerable.
Eggs, red meat and dark green vegetables provide iron, but people following restricted diets may find it harder to consume enough. One Brazilian study estimated that up to half of vegetarian women who menstruate could be iron deficient.
How coffee affects iron absorption
A cup of coffee consumed less than an hour after a meal can significantly reduce iron absorption, according to the material reviewed by experts. One study found that a single cup lowered absorption by between 39 and 90 per cent, depending on the strength and type of coffee.
Drinking coffee before eating does not appear to have the same effect. Researchers have advised leaving at least an hour between an iron-rich meal and a milky drink, particularly for people who already have an iron deficiency.
Milk may add to the problem because calcium can also reduce iron absorption. A study published in the 1990s found that more than 165mg of calcium, roughly the amount in half a glass of milk, reduced absorption from an iron-rich meal by up to 60 per cent.
However, the impact is thought to be most significant in people who are already deficient. Simply drinking coffee with food does not, by itself, mean someone will develop an iron deficiency.
Erin Deborah Waks, a 25-year-old journalist from London, said she was unaware of the possible link when she began suffering from severe tiredness late last year. She had a history of heavy periods and was drinking coffee with breakfast and lunch in an attempt to improve her energy.
“I felt tired and drained all the time, leaving nights out with friends early,” she said. “Last year I ran a half marathon – this year even a 10k would wipe me out for a whole afternoon.”
After months without improvement, Ms Waks visited her GP. A blood test showed that her iron levels were low and she was prescribed Ferrograd C, an iron supplement used to treat iron-deficiency anaemia.
“The doctor asked me if I drank coffee with meals and explained how it can affect iron absorption. I said I do – often twice a day,” she said.
“It made complete sense – but I was surprised nobody had told me this before, especially as I had been iron deficient in the past.”
Caffeine, sleep and tiredness
The warning comes as experts also examine the longer-term effect of caffeine on energy levels. Caffeine produces a temporary feeling of alertness by blocking adenosine, a compound involved in signals that tell the brain when it is tired.
When the effect wears off and adenosine builds up again, people can experience a sudden bout of tiredness. Regular consumption can also lead to tolerance, meaning more caffeine is needed to achieve the same alertness and potentially creating a cycle of poorer sleep and exhaustion.
A review using brain scans by experts from Wroclaw Medical University in Poland found that caffeine reduced the amount of restorative deep sleep participants obtained, even when it was consumed early in the day. This was put forward as one possible reason coffee drinkers may remain tired despite sleeping for eight hours or more.
Research from Australian Catholic University found that 100mg of caffeine – about the amount in one filter coffee or a small latte – had no significant effect on sleep when consumed four hours before bedtime. The researchers stressed that the impact varies from person to person.
By contrast, 400mg, equivalent to four or five espressos, prevented participants from falling asleep easily and made their sleep less restorative. The effect was recorded even when the last dose was taken 12 hours before bed.
Professor Richards believes women should be screened for iron deficiency every three to five years from the age of 16. He has called for more frequent testing among those with a history of iron deficiency or anaemia, vegetarians and women who experience heavy periods.
